def iskadomatsu(S):
  return S.index(max(S)) == 1 or S.index(min(S)) == 1
N = int(input())
A = list(map(int, input().split()))
Count = 0
for i in range(N - 2):
  if iskadomatsu([A[i], A[i + 1], A[i + 2]]):
    Count += 1
print(Count)